The present invention relates to nigrosine dyes having high solubility in or compatibility with organic solvents and/or resins and to a process for preparing the same.
Nigrosine dyes (C.I. Solvent Black 5, C.I. Solvent Black 7 and C.I. Solvent Blue 7) are soluble in organic solvents and useful for coloring synthetic resins, printing inks, inks for marking pens and ball-point pens, jet printing inks, stamp inks, etc. These dyes also find characteristic use in inks for infrared absorption reading because of their infrared absorption characteristics, and furthermore as charge control agents for electrophotographic, or electrostatic image, developer toners due to their electrostatic characteristics.
Nigrosine dyes commercially produced at present and used generally include spirit-soluble dyes such as hydrochloride and lower fatty acid salts of nigrosine, and oil-soluble dyes such as alkali-treated nigrosine base and higher fatty acid salts of nigrosine base. However, these dyes are not fully or completely soluble in generally contemplated solvents for various uses, so that improvements have been made therein to overcome this drawback.
For example, for such purpose, it is known to subject a nigrosine and a fatty acid to reaction in an aniline solution (Published Examined Japanese Patent Application No. 28792/1965); to react a nigrosine with oleic acid fluoride in a dioxane solution in the presence of triethylamine (Published Examined Japanese Patent Application No. 7800/1971); to produce a long-chain alkyl-containing nigrosine with the use of a long-chain alkyl-substituted aniline or long-chain alkyl-substituted nitrobenzene in place of the aniline or nitrobenzene for the corresponding preparation of nigrosine (Published Examined Japanese Patent Application No. 3185/1966); to couple a diazonium salt with a nigrosine (Published Unexamined Japanese Patent Application No. 13831/1976); to prepare a sulfonamide derivative of a nigrosine (Publsihed Examined Japanese Patent Application No. 50773/1972); and to obtain an amine salt of nigrosinesulfonic acid (U.S. Pat. No. 2,990,405).
However, these processes and the resulting products still remain to be improved because it is difficult to remove remaining unreacted starting materials from the reaction mixture, or because the product is not fully soluble in organic solvents or compatible with resins for various desired uses.
Furthermore, conventional nigrosine dyes have the inherent drawback that inks prepared with use of the particular dye become viscous with the lapse of time. While the active hydrogen of the amino portion of the nigrosine undergoes condensation with an organic acid to give an acid amide derivative which is less likely to become viscous with the lapse of time, this derivative is still insufficient and unsatisfactory in stability when allowed to stand as formulated into an ink.